2 answers

I can't understand, why this is still broken because since a few months this problem is reported.

The relevant bug report is in this sage-support thread, which also lists the relevant bug tracking tickets. The long delay from when a bug is first reported to the time the bug is fixed depends on many factors. But the delay is often a result of finding someone willing to volunteer to fix the bug and another person to volunteer their time to review the bug fix. Fortunately, the relevant tickets (#9394 and #9834) have received positive reviews. This means that you can most likely expect the fix to be in Sage 4.6.